/Engine/Source/Runtime/GeometryCore/Public/Selections/MeshVertexSelection.h
Grow selection outwards from seed vertex, until it hits boundaries defined by vertex filter.
void FloodFill ( const [TArray](API\Runtime\Core\Containers\TArray)< int > & Seeds, const [TUniqueFunction](API\Runtime\Core\Templates\TUniqueFunction)< bool(int)> & VertIncludedF )